Method and device for testing coins

ABSTRACT

Disclosed is a method and device for testing coins which are placed in a coin acceptor unit and which are displaced in front of an image sensor consisting of lines and columns, whereby said image sensor records an image of the coins that are to be tested. At least one of the front columns in the direction of movement of said coins and/or at least one line of the image sensor captures parameters, which in conjunction with the temporal detection information, are used to provide information on the movement of said coins. It is determined independently from said parameters when the coin will appear in a desired overlap area for recording, whereby the image sensor is shifted into an activation mode of the columns and lines of the overlap area and recording is triggered.

BACKGROUND OF THE INVENTION

The invention relates to a method and a device for testing coins, inwhich the image of the coin is detected using an image sensor.

In the process of recognising the embossing on coins there is a knownway of using photographic image sensors which usually have pixelsarranged in columns and lines. Here it is necessary to determine thecorrect moment of the recording of the moved objects i.e. the coin (herethe term “coin” is used to denote also tokens or counters or the like).One problem is detecting the coin in its unrestricted course of movementand monitoring the run of the coins only with the image recording systempresent or the image sensor. During the dynamic behaviour of a coin asit passes an image sensor and the production of an image by the opticalimage sensor, exact analysis of the times of passing through the imagingarea and the recording speed of the sensor must be made. It is crucialto determine the correct value for the exposure time and the moment ofthe recording. Although it is possible in special cases, it is not to beexpected that the coin will move through the recording area of the imagesensor at a constant speed and certainly will not stay there for a shorttime at all. There are four time areas to be examined, namely the run-inof the coin into the sensor area, the recording/exposure time, the datatransfer or transmission for processing the image in an evaluationdevice and the image processing, analysis and evaluation. Whilst for thefourth time period no fixed time value is given, apart from the maximumtime of the entire process, the first three time periods are extremelytime-critical.

Run-in times for selected coins were determined, the run-in time beingdetermined as the time from the appearance of the edge of the coin inthe recording area of the image sensor up to complete detection of thecoin by this recording area. The measured run-in time was between 4.5and 9.9 ms and that of 0.01, 0.10, 1 and 2 Euro coins was respectively4.9, 5.9, 6.99 and 7.71 ms. The aimed-at diameter range of the coins tobe measured is between 15 mm and 33 mm. Measurements in real coincheckers produced a maximum coin speed of 3 m/s. With the given timeconditions it is inconceivable to follow the run of the coin up to thecorrect recording position by cyclical scanning of the image. Moreoverin such a case the data transfer times from the image sensor to theoperating processors is much too long.

SUMMARY OF THE INVENTION

The object underlying the invention is to create a method and a devicefor testing coins using an image sensor to record an image of the cointo be tested, in which the moment of the recording of the image of thecoin or respectively the location of the recording is reliablydetermined and with which the data transfer times from the image sensorto the evaluation device are minimised.

This object is accomplished according to the invention by the featuresof the main claim and the subordinate device claim.

The invention exploits the capability of image sensors to select justpartial areas. Since the scanning speed of the individual pixels isindependent of their number, the transfer speed can be assumedpractically proportional to the number of points to be selected. Becauseonly at least one front column in the direction of movement of the coinand/or at least one line of the image sensor detect parameters of thecoin, which together with the temporal detection information provideinformation about the movement of the coin, and because in dependence onthese parameters and the temporal information it is determined when thecoin will appear in a coverage area, desired for recording, of the imagesensor, the image sensor being switched into activation of the columnsand lines of the coverage area and the recording being triggered, it ispossible to monitor the movement of the coin and to calculate exactlythe moment of the actual recording of the image of the coin, and as aresult of the activation of only the coverage area of the coin with theimage sensor, the time for reading out the image data is reduced.

Advantageous developments and improvements are possible due to themeasures quoted in the subordinate claims.

Through detection the apex of the coin by the at least one front columnin the direction of movement, the diameter of the coin can bedetermined, via which information can be provided about the height andwidth of the coverage area.

By scanning the front edge and the apex of the coin and the temporalinformation of the scanning and the diameter of the coin, the speed ofthe coin can be calculated in a simple manner, and especially in thecase of small coins which run slowly this speed information is alreadysufficient to fix the moment of the recording, since the recording areaof the image sensor is somewhat larger than the coin surface and thusrunning out of the sensor area without being checked is unlikely.

It is especially advantageous, after detection of the apex of the coin,to activate at least one line of the image sensor at the level of halfthe diameter, and to scan the front edge of the coin a number of times,since the speed and/or the acceleration of the coin can be calculatedexactly as a function of the scanning times and the distances covered.Thus the recording moment can be determined exactly even if the coinexperiences a delay or acceleration in the course of its run-in.

It is advantageous that as the coin runs through the at least onecolumn, the height pattern of the coin is detected and evaluated,grooves being recognised where discontinuities are present in the heightpattern.

An illumination device is advantageously provided which is activated ina pulsed manner at the moment of the recording, and thus goodillumination can be achieved as a result of the fixing of the moment ofthe recording, it being possible to determine the length of theillumination as a function of the speed of the coin.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are represented in the drawings and areexplained in greater detail in the following description. The figuresshow:

FIGS. 1-4 different states of movement of the coin in relation to animage sensor, and

FIGS. 5 and 6 a schematic illustration of the scanning of milled coins.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The device according to the invention is installed in a coin checker,preferably in the coin channel, in which the other measuring systems ofthe coin checker are also present, and the described device can beconfigured as a sub-system of the coin checker control system. Thedevice has an image sensor, the term “image sensor” being intended tocover the entire recording device with lens system. In addition, anilluminating device is provided which is associated with the imagesensor and which has a flashlight function, i.e. generates pulsedillumination of the coin surface.

A device according to the invention is represented schematically in FIG.1 and has the image sensor 2 arranged in the region of a coin track 1,with an appropriate lens system as well as an evaluation unit 3, whichis a constituent part of the coin checker control system, and anillumination assembly 4. The recording device configured as the imagesensor 2 is so set with the lens system that a specific visual field anda specific focus area are preset, and a coin 5 to be photographed shouldbe arranged in this area so that no optical distortions or obscurationoccur. The image sensor 2, the illustration of which shows the coveragearea, is provided with a large number of columns and lines which areformed from pixels and connected to the evaluation unit 3 and which maybe triggered individually or in areas by the evaluation unit 3 for theirinitialisation and activation for the process of reading out the datafrom the sensor as well as for the actual recording. The recording isthe process of “electronically fixing” the optical image, i.e. theoptical function as charge carrier is taken over with an electronic“shutter”. This happens in as short a period of time as possible inorder to avoid movement blurs. As the data are being read out of thesensor, the coin is already moving forward. With the triggering of thelines and columns for the recording, the illumination device 4 is alsotriggered.

So that an assessable recording of a coin 5 can be achieved, the momentof the recording, based on the movement parameters of the incoming coin5, must be determined via the evaluation unit 3 at the desired measuringposition or at the desired recording location. To this end, in thepreferred embodiment at the beginning of the detection only the firstcolumn 7 of the image sensor 2 in the direction 6 of movement of anincoming coin 5 is activated, the pixels of this first column 7 beingcontinuously read out by the evaluation unit 3 and the run-in of thecoin being awaited. As the coin 5 enters the image sensor, the frontedge is detected by the column 7 and recognised by the evaluation unit3, which activates a height check which is intended to recognise theapex of the coin.

On reaching the apex, according to FIG. 2, the evaluation unit 3determines the diameter of the coin 5 which is stored as the firstmeasured value of the system. The desired coverage area is fixed fromthe diameter.

At this point in time, a first assessment of the run-in speed of thecoin is possible since a speed can be calculated from the moment ofscanning the front edge, the moment of scanning the apex and from thediameter. In the simplest case, i.e. if certain indistinctness isadmitted, this information is already sufficient to fix the moment ofthe recording, which can be calculated from the speed and the desiredmeasuring position. This is true in particular for small coins which runslowly, since the desired recording area 8, represented in broken lines,in this case covers most of the coin surface and thus the coin isunlikely to exit from the sensor area without being checked. If howeverit is to be expected that the speed will alter as the coin runs in,additional checking of the passage of the coin is necessary.

For this additional checking of the passage of the coin, reference ismade to FIG. 3, in which a pixel line 9 on the centre line relative tothe diameter of the coin 5 is activated. This activation is undertakenby triggering the evaluation unit 3 after recognising the diameter ofthe coin 5. In this case, the first scanning line 7 can be deactivated.Scanning the front edge of the coin 5 on the centre line providescontinuously the progress of the coin as it runs through the system.With the temporal information of the scanning of the front edges and thedistances respectively covered, the respective speed and, if desired,the respective acceleration can be determined, which then serve todetermine the time of the coin's arrival at the measuring position. As afunction of this temporal prediction and/or once the coin 5 hascompletely entered the designated recording area 8, the lines andcolumns of the image sensor are initialised in the height and widthpredetermined by the diameter of the coin 5, as the coverage area at therecording location, by the evaluation unit 3, and triggered at thepreviously calculated point in time. This is shown in FIG. 4, in whichthe coin is shown in the desired coverage area 10 with the image sensor.Due to the previously ascertained diameter of the coin and the time atthe measuring position, determined from the speed or acceleration, thecoverage area of the image sensor 2 which is to be recorded can beselected in an optimum manner.

Depending on the coin size, the coverage area or recording area islimited by the evaluation unit 3 triggering the lines and columns, thetime for reading out the image data being reduced to a minimum. If theevaluation of the data is matched to this, in order to save space in theworking memory, even the areas of the coverage area 10 which are locatedoutside the circular image can be suppressed, i.e. the signals fromthese areas are not passed on by the evaluation unit 3.

During the recording according to FIG. 4, the illumination device 4 issimultaneously triggered by the evaluation unit 3, which also determinesthe exposure time from the previous information about the speed and thediameter. For reproducible illumination, which is as free of shadows aspossible, of the coin surface during the recording, a diffuse, even andas bright as possible illumination of the coin is required. This isactivated as already mentioned only at the moment of the recording andalso in a pulsed manner on account of the high consumption of current.

The illumination for the recording can take the form for example of aplurality of light diodes arranged in a ring with a diffuse reflector.

According to present knowledge, the exposure time of the recording mustbe controlled with the aid of deliberate control of the illumination.This is necessary since circulating coins have a very strong spectrum ofcontamination and oxidation and thus reflection capability. Furthermore,for cost reasons, a lens system with a fixed aperture is usually used.

On account of the expected high running speed of the coin, controllingexposure by the exposure time has to be excluded if possible. Theexposure must be kept as short as possible in order to avoid movementblurs. There remains the possibility of controlling the current supplyto the illumination elements or to a gain control of the image sensor.

In addition to the illumination for the actual recording, illuminationfor checking the coin run-in is required, which can be configured aspoint-source or linear illumination with a lower light intensity orenergy than the main illumination in that area.

Independently of the demands on the illumination for recording the coin,therefore other illumination techniques can be used in the run-in area,by means of which additional measured values can be obtained, e.g. flatdirectional, in order to ascertain embossing depths with shadowformation, multi-coloured illumination for recognising two-colouredcoins, coloured illumination for recognising the material.

It must also be considered that the illumination for the run-in checkhas to be activated a number of times if not even constantly over theentire period of the coin run-in.

Naturally this illumination for the run-in check is controlled by theevaluation unit 3, which basically monitors the run-in. Here it can alsodetermine the average brightness of the coin which is used forcontrolling the exposure.

In certain circumstances, the method can be simplified to remove therecording time by additional checking of the passage of the coin as perFIG. 3 being dispensed with. Then monitoring only via the first columnis achieved, the moment of the passage of the first edge and the momentof the passage of the apex, which however cannot be fixed exactlybecause of the tangential run-in, being determined. The moment of thepassage of the rear edge can possibly also be detected. As above, thespeed can be determined by using the diameter and the recording momentcan be predicted from the speed, and in addition the moment of thepassage of the rear edge can be used for checking. The simplifiedscanning is reliable if the boundary conditions are not so time-criticaland the coin movements are continuous enough for exact checking of thecoin's running not to be necessary.

As a support to the run-in check in the first column, a column withinthe scanning area 8 can also be scanned. The time of reaching thisposition can then be used together with the spacing of the columns indetermining the speed.

In certain cases, especially when the diameter ranges of the coins to bedetected are similar, monitoring only via one line can be envisaged. Butwith this monitoring there is the problem of fixing the correct positionof the line to be scanned. Therefore a compromise has to be made inrespect of precision. Otherwise in this method also the front edge andthe rear edge of the coin are detected, it being possible to determinethe central position of the coin with this information. In this type ofscanning, a larger scanning area of the image sensor is necessary.

There also exist image sensors which do not admit any freelypositionable selection of image data, but which make possible reading ofpixels in blocks or switching down to a much smaller resolution. Inthese cases too, the previously mentioned scanning by means of columnsand possibly lines can be carried out, the columns and lines then havinga reduced number of pixels.

In FIG. 5 and FIG. 6 is represented a so-called groove check, which canbe carried out with the preferred embodiment. The entry of the coin intothe image sensor or the measuring system is monitored by the rapidscanning of the first column, and the apex of the coin, i.e. itsdiameter, as mentioned, is determined. When the height pattern ischecked, discontinuities can be evaluated as grooves. With theappropriate mathematical correlation, the recognition of polygonal coinsis also possible.

As shown in FIG. 5, an enlargement of the upper coin edge 11 as it runsthrough the first column 7 of the image sensor 2 is illustrated. In thesimplest case, only one column is scanned and the repeated change of theuppermost pixel as the apex runs through is recognised as milling.Knowing the speed of the coin, the width of the grooves can also bededuced.

An expanded form having two adjacent columns 7, 12 simplifies therecognition of a groove since then two adjacent pixels respectivelysupply two negated signals. Their change shows the presence of millingon the edge of the coin 11. For the sake of simplicity, in FIG. 6 thestarting point is a groove depth of the dimensions of one pixel of theimage sensor. Depending on the resolution of the image sensor, however,the groove depth can also be a plurality of pixels. Then the groovedepth becomes a measurable feature of the coin.

1. Method for testing coins which are inserted into a coin checker andrun past an image sensor which has lines and columns and which recordsan image of the coin to be checked, comprising the steps of: providinginformation about the movement of the coin with at least one of thefront columns in the direction of movement of the coin and at least oneline of the image sensor detecting parameters, together with temporaldetection information; determining when the coin will appear in acoverage area of the image sensor as a function of the parameters forrecording; switching the image sensor into activation of the columns andlines of the coverage area; and triggering the recording; scanning thefront edge and the apex of the coin by at least one of the front columnsin the direction of movement; determining the diameter of the coin fromthe scanning of the apex; and after detecting the apex of the coin, thenactivating at least one line of the image sensor at the level of halfthe diameter.
 2. Method according to claim 1, further comprising thestep of calculating the speed of the coin as a function of the momentsof scanning the front edge and the apex as well as of the diameter ofthe coin.
 3. Method according to claim 1, further comprising the stepsof scanning in each case the front edge of the coin during run-in andcalculating at least one of the speeds and accelerations of the coins asa function of the scanning moments and distances covered.
 4. Methodaccording to claim 1, further comprising the step of determining atleast one of the time of the arrival of the coin for the recording andthe position of the coin for the recording as a function of the speedand the acceleration of the coin.
 5. Method according to claim 1,further comprising the steps of detecting and evaluating a heightpattern of the coin as the coin runs through the at least one column andevaluating discontinuities in the height pattern as grooves.
 6. Methodaccording to claim 5, further comprising the step of determining thegroove width once the coin speed is known.
 7. Method according to claim1, further comprising the step of activating an illumination device forilluminating the coin in a pulsed Manner at the time of recording. 8.Method according to claim 1, further comprising the steps of scanningthe front edge of the coin by an additional column, which is arranged inthe direction of movement of the coin offset to the at least one frontcolumn, and calculating the speed of the coin as function of the timesof scanning the front edge of the coin and the distance between thecolumns.
 9. Method according to claim 1, further comprising the steps ofscanning the front and the rear edges of the coin-by at least one line,activating the columns and lines of the coverage area and triggering therecording as a function of the times of the scanning.
 10. Method fortesting coins which are inserted into a coin checker and run past animage sensor which has lines and columns and which records an image ofthe coin to be checked, comprising the steps of: providing informationabout the movement of the coin with at least one of the front columns inthe direction of movement of the coin and at least one line of the imagesensor detecting parameters, together with temporal detectioninformation; determining when the coin will appear in a coverage area ofthe image sensor as a function of the parameters for recording;switching the image sensor into activation of the columns and lines ofthe coverage area; and triggering the recording; scanning the front edgeand the apex of the coin by at least one of the front columns in thedirection of movement; determining the diameter of the coin from thescanning of the apex; scanning the front edge of the coin by anadditional column, which is arranged in the direction of movement of thecoin offset to the at least one front column; and calculating the speedof the coin as a function of the times of scanning the front edge of thecoin and the distance between the columns.
 11. Method for testing coinswhich are inserted into a coin checker and run past an image sensorwhich has lines and columns and which records an image of the coin to bechecked, comprising the steps of: providing information about themovement of the coin with at least one of the front columns in thedirection of movement of the coin and at least one line of the imagesensor detecting parameters, together with temporal detectioninformation; determining when the coin will appear in a coverage area ofthe image sensor as a function of the parameters for recording;switching the image sensor into activation of the columns and lines ofthe coverage area; and triggering the recording; scanning the front edgeand the apex of the coin by at least one of the front columns in thedirection of movement; determining the diameter of the coin from thescanning of the apex; scanning the front and the rear edges of thecoin-by at least one line; activating the columns and lines of thecoverage area; and triggering the recording as a function of the timesof the scanning.
 12. Device for testing coins which are inserted into acoin checker, said device having an image sensor which has lines andcolumns for recording an image of the coin to be checked and passing theimage sensor, and an evaluation device connected to the image sensor, atleast one of the front columns in the direction of movement of the coinand at least one line of the image sensor being activated to detectparts of the coin, and the evaluation device determining the desiredcoverage area from signals of the image sensor and associated temporalinformation and triggering the image sensor to record, wherein theevaluation device determines the apex and thus the diameter of the coinfrom the signal of the at least one front column, and wherein theevaluation device activates the lines and columns of the image sensorindependently of at least one another and in areas.
 13. Device accordingto claim 12, characterised in that an illumination device is connectedto the evaluation unit for pulsed illumination of the image sensor atthe time of recording.
 14. Device according to claim 12, characterisedin that an illumination device is provided to illuminate the coin for arun-in check.